This invention relates to a pump for circulating electrolyte within an electrochemical cell. More particularly, this invention relates to a completely in-cell pump that utilizes battery gas to lift solution of an electrolyte body from near the bottom and mix it with solution near the top, thereby vertically stirring the electrolyte body.
During deep cycling of a lead-acid cell comprising a body of an aqueous sulfuric acid electrolyte, solution near the bottom tends to become more concentrated and denser than solution near the top. This electrolyte stratification reduces cell capacity, at least in part, because of electrolyte starvation near the top. Thus, to maintain cell performance, it is necessary to stir the electrolyte body. A common practice is to apply a relatively large overvoltage to the electrodes during recharging to create many small gas bubbles that rise and agitate the electrolyte. However, freely rising bubbles are relatively ineffective for stirring the denser, bottom electrolyte. Thus, excessive gassing is required, which wastefully consumes electrolyte and enhances spalling of the active electrode material. It has also been proposed to circulate the elctrolyte using an air lift wherein air is intermittently pumped into an open-end vertical tube immersed in the electrolyte. The air lift is more efficient than free bubbles, but complicates battery operations and requires an air pump outside the cell with connections to the tube.
It is an object of this invention to provide a self-stirring battery cell construction having a liquid electrolyte body and employing battery gas to lift solution from a bottom region of the electrolyte body to a top region, thereby vertically stirring the electrolyte body.
It is a further object of this invention to provide an electrolyte circulation pump adapted to be enclosed completely within a battery container and to operate therein, without supplemental external equipment, to reduce electrolyte stratification. The pump collects battery gas from relatively small bubbles that are produced during cell operations and releases relatively large bubbles in an electrolyte conduit, which bubbles rise and carry liquid from the bottom to the top of the electrolyte body more efficiently and more effectively than freely rising small bubbles.